1. Field of the Invention
The present invention relates to a device having a crystalline thin film of oxide complex compound (hereinafter referred to as complex compound), more specifically, relates to improvement of crystallinity for the crystalline layer of complex compound.
2. Description of the Prior Art
In identifying dielectric properties spontaneous polarization based on permanent dipole moment and change in polarization when applying an electric field are referred to as ferroelectric properties. Among the ferroelectric properties, a substance with a chemical formula of ABO3 with generates spontaneous polarization by displacement from an equilibrium point is especially referred to as ferroelectric properties with perovskite structure. Lead zirconate titanate (hereinafter PZT), has ferroelectric properties with perovskite structure is binary system solid solution porcelain of PbZrO3xe2x80x94PbTiO3. A ferroelectric thin film which utilizes PZT is applied to various semiconductor devices such as ferroelectric memory and ferroelectric capacitors and others.
Details of a ferroelectric capacitor 40 will be described below with reference to FIG. 1. As illustrated in FIG. 1, the following layers are formed consecutively on silicon layer 2, such as silicon oxide layer 4, lower electrode 13, PZT thin film 8 and upper electrode 10. In this configuration, the upper electrode 10 is made of platinum, and lower electrode 13 consists of titanium layer 5 and platinum layer 6.
Electric characteristics of PZT thin film 8 are illustrated in FIG. 2 as a hysteresis loop. In FIG. 2, the ordinate shows polarization P and an axis of abscissas shows electric field E. The PZT thin film 8 is polarized into almost same direction of the given electric field as symbolized by P1 in the FIG. 2, when applying a larger voltage than a coercive voltage to the lower electrode and upper electrode. Note that the coercive voltage is a voltage which has enough potential to erase remanent polarization from the ferroelectric layer. This polarization status will remain even when the coercive voltage is cut off, as symbolized by Q1 in FIG. 2.
On the other hand, in order to erase remanent polarization from the ferroelectric layer, a voltage is applied to the lower and upper electrode in an opposite direction against the voltage applied previously to the electrodes. As a result, the polarization is turned as symbolized by R1 in FIG. 2. At this time, the polarization remains as it is even if the voltage is cut off as symbolized by S1 in FIG. 2. Electric field E in FIG. 2 which extends Ec2 andxe2x80x94Ec2 functions as a diverging point of the polarization.
Since PZT thin film has the above described electric characteristics, PZT thin film 8 is applicable to manufacture ferroelectric nonvolatile memories and ferroelectric nonvolatile capacitors.
However, ferroelectric capacitor manufactured in the prior art has the following problems. In manufacturing a ferroelectric capacitor thermal treatment is carried out on the lower electrode 13 for improvement of both crystallinity and orientation of the PZT thin film 8, when sputtering is carried out during the process of forming the lower electrode 13.
The thermal treatment prevents utilization of the xe2x80x9clift-offxe2x80x9d method for forming the lower electrode 13 in a predetermined shape, because of the nature of the xe2x80x9clift-off xe2x80x9d method. The xe2x80x9clift-offxe2x80x9d method is carried out under the following steps. First, photo resist covers several portions of a substrate where electrodes are not formed. A polysilicon layer is formed on the substrate and the photo resist. The polysilicon layer where formed on the photo resist is removed together with the photo resist when the photo resist is removed, so that the lower electrode remains on the substrate.
Although photo resist stands until 130xc2x0 C., the temperature of the photo resist exceeds 130xc2x0C. when carrying out sputtering. Therefore, the xe2x80x9clift-offxe2x80x9d method is not applicable to form the lower electrode.
To resolve this issue and improve crystallinity and orientation of PZT thin film 8, the thermal treatment is carried out to the lower electrode 13 when sputtering is carried out, and an xe2x80x9cion-millingxe2x80x9d method is utilized to form the lower electrode 13 in a predetermined shape. A result of utilizing the xe2x80x9cion-millingxe2x80x9d method is damage to the surface of the substrate due to a low selective ratio.
In other words, it is not possible for the ferroelectric capacitor formed by previous methods to realize the improvements of both crystallinity an orientation of a PZT thin film 8 without damaging the surface of the substrate.
It is an object of the present invention to provide a device having a crystalline oxide layer of a complex compound which can form a crystalline thin film with a high orientation without damaging the surface of the substrate, thereby solving the above mentioned problems.
The present invention is a device having a crystalline thin film of complex compound comprises:
a) a first electrode having a lower layer of tantalum and an upper layer which contains platinum located on the lower layer;
b) a crystalline thin film of complex compound located on the upper layer; and
c) a second electrode located on the crystalline thin film.